Knowledge Bank

When a Fresnel rhomb is used for sub-Doppler Lamb dip spectroscopy, the returning beam is precisely collimated with the ongoing beam. Therefore we can use a multiple reflection mirror system to increase the path length and thus the sensitivity. Such a technique has been incorporated into our $CO2$ laser microwave modulation sideband system. The increased sensitivity has made it possible to resolve some of the hyperfine structure of the band of $NH3$ which was previously not resolved. The application of the method to other molecules, such as $SiF_{4}, $SE and $PH2$, will also be presented.